The present invention relates in general to ignition systems for internal combustion engines and more particularly to contactless ignition systems providing a direct replacement for mechanical ignition points.
The mechanical ignition points used in conventional ignition distributors for internal combustion engines are of limited reliability. Their limited reliability is due to pitting and burning of the contact points and wear of the contact point lifter in engagement with the cams on the end of the distributor shaft. The points must be checked at regular intervals and the gap reset when necessary. The contact surfaces require refacing or cleaning at regular intervals, and the points must be replaced when excessively pitted or worn. Failure of the capacitor normally connected in parallel across the contact points, such as shorting causes complete ignition failure. Cut-off of the capacitor or defective grounding causes excessive sparking at the points, resulting in pitting, burning and rapid deterioration of the point contact surfaces. Non-conductive, or poorly conductive, dirt between the point contact surfaces causes complete failure of the ignition system.
Another disadvantage associated with conventional mechanical ignition points which causes malfunction at high RPM of the internal combustion engine is due to the rebound or floating of the points caused by inertia and deflection of the elements when the movable breaker points are rapidly oscillated by the rapidly rotating cam of the distributor shaft.
Attempts have been made in the past to remedy some of the disadvantages associated with conventional mechanical ignition points for automotive ignition distributors, such as using electromagnetic pickups, as disclosed in U.S. Pat. No. 3,787,432, or replacing the mechanical ignition points with a photoelectric system comprising in combination a light source, a photoelectric pickup element and a rotatable shutter in the form of a slotted disk or drum placed between the light source and the photoelectric pickup element, as disclosed for example in U.S. Pat. Nos. 3,792,261, 3,621,826, 3,421,488, 3,422,804, 3,235,742, 3,386,000 and 2,084,267. However, the latter arrangements require the designing of an entirely new ignition distributor with appropriate means for driving the slotted disk or drum. Electromagnetic pickup devices have poor reliability and do not provide accurate timing of the ignition pulses.
The present invention, by contrast, permits to provide a low cost direct replacement for conventional mechanical ignition points for engines already equipped with conventional ignition systems. The present invention requires no modification to the conventional ignition systems and it provides a simple standard unit adapted for mounting, through an adapter plate, on the distributor breaker plate instead of the mechanical points and capacitor, without any other modification or adaptation of the distributor such that the conventional ignition advance mechanism, the distributor rotor and cam and the distributor cap are utilized as parts of the ignition system. Furthermore, the present invention is useful in solid state or electronic ignition systems, and may be used in combination with the high frequency ignition system disclosed and claimed in U.S. Pat. No. 3,900,786.